Lab 8 NMO and Residual Velocity Analysis Objectives: Apply NMO CMP Stack the NMO (for later comparison) Compute Residual Statics Apply Residual statics on NMO Stack the Residual NMO Compare with residual stack with non-residual stack Apply residual on non-NMO data Run velzone on residual applied data Sumit VermaBryce Hutchinson NMO flow 1. I chose bandpass SC scaled data as the input for NMO because I thought that looked best. You may choose the volume you believe looks best. 4. For NMO, click File and select the velocity file that you created when you picked velocities in a previous lab. Here we are applying NMO in order to flatten the data. This is the first step necessary to create a brute stack of the data volume. 3. For NMO, Right click Input to access Data INPUT control Data/Header Selections. Set the CMP Bin to include all inlines and crosslines and set the increment to Make the sort CMP_NO Note variable CMP fold Mute cut 3. Click this icon to create the sort after you have designed it. NMO result 1. We will create a sort to show the NMO results Click the green plus to create a new sort 2. We will create a sort to show the NMO results Click the green plus to create a new sort This is will better display our results. 4. We Apply your sort through a simple input- output flow. Select the sort on the input. 1. Change the annotation at the top to display CMP and Absolute shot offset Take note of some of the discontinuity between traces in this image. We hope to improve this with residual statics. Stack flow 1. Use the NMO file as an input for CMP stacking. Sort it by CMP_NO Do not worry about changing any of the settings in CMP Stack at this point in time. This file may take a while to run so take this time to consider what stacking is doing. Source:Incorrect velocity analysis will result in a poor stack. This is why we must improve our velocity model. Brute Stack Stack Power 1. Choose NMO (prestack) as the input. 2. Click file in the Stack Power dialog box and type in a name to save your file by. Residual Statics 1. Use the prestack NMO data as the input for residual statics. 2. Choose the file created in stack power as the input for Read Static Shifts 3. Select Static_Total as the defined header static in Apply Static Shift dialog. 4. Create the same sort we did in slide 3 for comparison Residual Statics for comparison 1. Change the annotation at the top to display CMP and Absolute shot offset After 1. Change the annotation at the top to display CMP and Absolute shot offset Take note of some of the discontinuity between traces in this image. We hope to improve this with residual statics. Before Residual Statics for comparison Before Stack residual statics Use the CMP stack flow to stack both the residual applied NMO and original NMO volumes in order to compare the difference the NMO makes in a stacked volume. Brute Stack CMP Stack after residual statics correction Areas we can still improve upon. Areas of improvement. Apply residual statics to pre-stack data 2. Set the input as the original band pass data we used in the beginning of the lab. 1. Run the apply statics flow again. Processing Workflow We iteratively compute the residual statics and do velocity analysis on finer grid. Dowdell, 2013 Perform Velocity Analysis 1. Use the residual applied volume as the input for the velocity analysis. Pick velocity of 5x5 grid 1. Use previous velocity picks as a guide. Save a copy of your file so that you dont overwrite the original. 2. Then open your velocity copy and use it as a guide to pick this new finer grid. Pick velocity on a 5x5 grid Pick velocities only on panels that have more than 50% of traces present. X Velocity picking should start at higher supergather sizes then work down to finer and finer grinning. We started with 8*8 super gather and 10*10 picking. The goal of residual statics is to tweak your velocity model to be as detailed as possible. We do this by iteratively picking velocities on finer and finer grid sizes. Lets see what velocity picking on finer grid is similar to increasing pixels of a photo. What is this ? Oh a guy? Bryce? Acknowledgement ! Thang Ha and Marcus Cahoj